Question

A textile mill wishes to establish a control procedure on flaws in towels it manufactures. Using an inspection unit of 50 units, past inspection data show that 100 previous inspection units had 850 total flaws. What type of control chart is appropriate? Design the control chart such that it has two-sided probability control limits of α=0.06, approximately. Give the center line and control limits.

Answer 1

The appropriate control chart for the textile mill is the p-chart. The center line is 8.5 flaws per unit, and the control limits can be calculated using the formula LCL = p - Z * sqrt((p(1-p)) / n) and UCL = p + Z * sqrt((p(1-p)) / n).

Step-by-step explanation:

The appropriate control chart for the textile mill to establish a control procedure on flaws in towels is the p-chart. This chart is used to monitor the proportion of defects in a process. The center line of the p-chart is calculated using the formula p = defects / units inspected. In this case, the center line is 850 / 100 = 8.5 flaws per unit. The control limits are calculated using the formula:

• Upper Control Limit (UCL) = p + Z * sqrt((p(1-p)) / n)
• Lower Control Limit (LCL) = p - Z * sqrt((p(1-p)) / n)

Where p is the proportion of defects, Z is the Z-score corresponding to the desired level of significance (such as 0.06), and n is the number of units inspected. The Z-score can be calculated using a Z-table or a statistical software. The control chart is used to determine if the process is in control or if there are any special causes of variation that need to be addressed.

Answer 2

•A c-chart is the appropriate control chart

• c' = 8.5

• Control limits, CL = 8.5

Lower control limits, LCL = 0

Upper control limits, UCL = 17.25

Step-by-step explanation:

A c chart is a quality control chart used for the number of flaws per unit.

Given:

Past inspection data:

Number of units= 100

Total flaws = 850

We now have:

c' = 850/100

= 8.5

Where CL = c' = 8.5

For control limits, we have:

CL = c'

UCL = c' + 3√c'

LCL = c' - 3√c'

The CL stands for the normal control limit, while the UCL and LCL are the upper and lower control limits respectively

Calculating the various control limits we have:

CL = c'

CL = 8.5

UCL = 8.5 + 3√8.5

= 17.25

LCL = 8.5 - 3√8.5

= -0.25

A negative LCL tend to be 0. Therefore,

LCL = 0